Physics Guides

	Black Holes - Not So Black
	Black holes may not be as eternal as they are made out to be. The matter that goes into a black hole has no hope of ever coming back out, but they are in a way recycled into what is called Hawking radiation that the black hole emits.
	To explain this fully you have to go down to a quantum level. On a plank scale length virtual particles are constantly created and destroyed. These particles are created in particle/anti-particle pairs (an antiparticle is the antimatter counterpart of a particular particle, such as the positron for the electron) and they arrise from quantum fluctuations where the energy to create the particles is temporarily 'borrowed', normally these two particles would then come in contact and be annihilated giving back the energy.
		This picture shows how the in the vicinity of a black hole, the virtual particles can be split up, hence looking like the black hole emitted the particle
	Where this fits in to black holes radiating is that at the event horizon of a black hole it is possible for one of the two particle to be sucked in while the other escapes, leaving nothing for it to annihilate with! So looking at a black hole it does not appear to be completely black it infact radiates particles, this has been named Hawking Radiation by its discoverer Stephen Hawking who proposed the controversial finding in 1974. This leads to some profound consequences, if a particle that was supposed to be annihilated has escaped then where did the energy needed to create it come from? Well Hawking proposed that it tunneled out of the black hole, because of Einsteins equation relating mass to energy ( E = mc^2 ) you can see that if the black hole has given up some energy it must then reduce in mass. So to an outside observer it would appear that the black hole just emitted a particle and is now shrinking as this continues to happen! The rate at which black holes radiate is inversely proportional to thier size, so a larger black hole shrinks slower than a smaller one. This also means that micoscopic black holes would let off a tremendous amount of energy - a possible power source maybe? The only problem is that a black hole any larger than the mass of the moon would be absorbing more radiation (CBR) than it is emitting hence been at an equlibrium of about 2.7 degrees kelvin, pretty damn cold! But scientists are confident that tiny primodial black holes created in the early universe would give off more than they emit hence losing mass and being detectable. There are teams currently searching the skies for them now. Jayden Newstead

Black Holes - Not So Black